Pyrazole Complexes as Anion Receptors

Abstract

The behavior of the receptors [Re(CO)3(Hdmpz)3]BAr'4 (Hdmpz = 3,5-dimethylpyrazole) (1) and [Re(CO)3(HtBupz)3]BAr'4 (HtBupz = 3(5)-tert-butylpyrazole) (2; Ar' = 3,5-bis(trifluoromethyl)phenyl) toward the anions fluoride, chloride, bromide, iodide, hydrogensulfate, dihydrogenphosphate, nitrate, and perrhenate was studied in CD3CN solution. In most cases, the receptors were stable. Anion exchange was fast, and binding constants were calculated from the NMR titration profiles. The structure of the adduct [Re(CO)3(HtBupz)3] x NO3 (3) was determined by X-ray diffraction. Two pyrazole moieties are hydrogen-bonded to one nitrate oxygen atom, and the third pyrazole moiety is hydrogen-bonded to an oxygen atom of an adjacent nitrate, leading to infinite chains. The structure of the adduct [Re(CO)3(Hdmpz)3]BAr'4acetone (4), also determined by X-ray diffraction, showed a similar interaction of two pyrazole N-H groups with the acetone oxygen atom. F- and H2PO4(-) deprotonate the receptors, and HSO4(-) decomposed 1. The structure of one of the decomposition products (5), determined by X-ray diffraction, is consistent with pyrazole protonation and substitution by sulfate.

Preparation and characterization of rhenium (I) tricarbonyl dithiocarbamate compounds; Re(CO)3(S2CNMe2)(L)

“…The average Re-N distance for 2 and 3 is 2.223(5) Å, comparable to the average value of 2.21(2) Å for the series of [Re-(CO) 3 L 3 ][PF 6 ] and Re(CO) 3 L 2 Br with N-heterocyclic base ligands [22]. The Re-N value of 2.173(10) Å measured for 4 is at the low end of the range of values, 2.17-2.20 Å, observed for comparable pyrazole complexes [30][31][32][33][34]. The Re-P distance for 5 is 2.470(3) Å [12].…”

Pyrazole Complexes and Supramolecular Chemistry

“…[68] With HSO 4 -, one of the pyrazole ligands was protonated, leading to the coordination of sulfate, to which the resulting pyrazolium cation, outside the first coordination sphere of the metal, is strongly hydrogen-bonded (Scheme 3a). With the fluoride anion, deprotonation of the NH group took place (Scheme 3b).…”

“…[68] Thus, the N-Re-N angles need to open somewhat to form the hydrogen bonds with the anionic guest. The difference from the compounds studied by the [ 64,65,68] ).…”

The effect of different ligand substituents on the chemistry of a zinc–pyrazole anion host

“…11 We and others have described anion hosts based on the [L n M(Hpz) 3 ] + motif, where [L n M] + is a transition metal fragment and Hpz is pyrazole or a substituted derivative of it (Scheme 1). 9 While several anion complexes based on this motif have been crystallographically characterised, [12][13][14][15][16][17][18][19][20] two systems have been studied particularly thoroughly. First is [ZnCl(Hpz tBu ) 3 ] + (Hpz tBu = 5-tert-butyl-1H-pyrazole), where the three pyrazole NH groups and tert-butyl substituents occupy one face of the coordination tetrahedron, forming a bowl-shaped cavity.…”

“…15,16 Rotation of one or two of the pyrazole groups at each zinc centre about their Zn-N bonds enlarges the cavities, allowing them to bind the larger anions. [18][19][20] Where available, crystal structures imply that guest anions associate with only two of the three N-H donors at the complex cation (Scheme 1D). [18][19][20] Where available, crystal structures imply that guest anions associate with only two of the three N-H donors at the complex cation (Scheme 1D).…”